A global system for mobile communications (GSM) scheme is a communication scheme of the second generation (2G) mobile communication system and employs a time division multiple access (TDMA) scheme. In the GSM scheme, IQ symbol data based on sampling at 270.833 kHz is used. That is, a symbol rate is 270.833 sps (samples/sec).
FIG. 1 is a diagram illustrating an example of a frame structure of a GSM scheme.
In the GSM scheme, one time slot is constituted by 156.25 symbols. That is, the one time slot is 156.25 symbols×1/270.833=576.9 μs.
In the GSM scheme, one TDMA frame is constituted by 8 time slots. That is, the one TDMA frame is equivalent to 576.9 μs×8=4.615 ms.
In the GSM scheme, one multiframe is constituted by 26 TDMA frames. That is, the one multiframe is equivalent to 4.615 ms×26=120 ms.
In the GSM scheme, one superframe is constituted by 51 multiframes. That is, the one superframe is equivalent to 120 ms×51=6.12 s.
In the GSM scheme, one hyperframe is constituted by 2048 superframes. That is, the one hyperframe is equivalent to 6.12 s×2048=12533.76 s.
A radio unit and a baseband unit (BBU) are included in a base station. The radio unit is also referred to as a remote radio head (RRH). In the GSM scheme, the RRH and the BBU are connected to each other with an interface dedicated to symbol transmission.
In recent years, third generation (3G) mobile communication schemes and so-called fourth generation mobile communication schemes have been widely used. Examples of the third generation mobile communication schemes include a code division multiple access (CDMA) scheme and wideband code division multiple access (WCDMA). Examples of the fourth generation mobile communication schemes include long term evolution (LTE) and LTE-Advanced. In third and later generation mobile communication schemes, an interface that connects an RRH and a BBU has been standardized. A common public radio interface (CPRI) is a known example of the standardized interface that connects the RRH and the BBU (see, for example, CPRI Specification V4.2 (September 2010)).
The CPRI is an interface standard for the so-called third and later generation mobile communication schemes.
In the third and later generation mobile communication schemes, IQ symbol data based on sampling at 3.84 MHz is used.
A frame transmitted via the CPRI will be described.
FIG. 2 is a diagram illustrating an example of a basic frame transmitted via a CPRI. FIG. 2 illustrates the case of 1228.8 Mbps. The horizontal axis in FIG. 2 represents time.
The length of a basic frame forming the basis of a frame transmitted via the CPRI is equivalent to 1 Tc=1/3.84 MHz=260.416667 ns. The basic frame includes 16 words. One word among the 16 words is a control word and the other 15 words are IQ symbol data.
In the CPRI, a hyperframe which is formed using 256 basic frames and a radio frame which is formed using 150 hyperframes have been standardized.